Structural reliability is a key factor in the design of wind turbine rotor blades. However, the use of composite materials in the blade structure and the many stochastic variables that are thus involved in the analysis makes the available probabilistic methods unattractive for integration in the design procedure. To overcome this, a numerical tool is developed for the probabilistic strength analysis of Fibre Reinforced Plastic (FRP) rotor blades. The stochastic nature of the anisotropic material properties is considered for the reliability estimation of the laminate and in turn the information is included in a pre- and post-processor of current aero-elastic codes. Copyright © 2009 John Wiley & Sons, Ltd.